The present invention relates to a tremolo unit for string instruments.
Tremolo units for string instruments are widely known and often installed in electric guitars. A tremolo unit increases and decreases the tension of the strings of a string instrument to make the sound of the instrument impressive. FIG. 11 illustrates a typical prior art tremolo unit 110 applied to a guitar. The tremolo unit 110 includes a base plate 111, string supports (bridge saddles) 121, a tremolo body (bridge) 120, a tremolo arm 125, and springs 130. The string supports 121 are pivotally attached to a body B of the guitar and support strings S at the top surface of the base plate 111. The tremolo body 120 has a tremolo block 122 extending inward of the body B below the base plate 111. The tremolo arm 125 is attached to the tremolo body 120 to pivot the tremolo body 120. The springs 130 are located between the tremolo block 122 and the body B. In cooperation with the tension of the strings S, the springs 130 keep the tremolo body 120 at an equilibrium position. The base plate 111 has knife edges 112 at one end. Stud bolts 115, each having a groove, are fixed to the body B. Each stud bolt 115 pivotally supports the corresponding knife edge 112 at the groove. Spring engaging member 135, to which the springs 130 are hooked, is fixed to the body B. The urging force of the springs 130 is adjusted by the spring bolts 135.
The tremolo unit 110 is constructed such that the tremolo body 120 is kept in equilibrium by the tension of the strings S and the urging force of the springs 130, which acts against the tension of the strings S. When the tremolo body 120 is pivoted by manipulation of the tremolo arm 125, the tension of the strings S is increased or decreased, which raises or lowers the pitch of each string S. When the arm 125 is released, the tremolo 120 returns to the equilibrium position and the pitch of each string S returns to the original pitch.
However, the equilibrium of the tremolo body 120 is extremely sensitive and affected by various factors. For example, friction at the pivot fulcrum, imperfect resilience of the springs 130, touching of the tremolo body 120 or the tremolo arm 125 by a guitar player, choking, flatter (fluctuation of sound due to an inertial force when the player abruptly releases the tremolo arm 125), and snap of the strings S may hinder the tremolo body 120 from returning to the equilibrium position after the tremolo body 120 is pivoted. This detunes the strings S. Another significant drawback of the tremolo unit 110 is the difficulty of tuning. Specifically, when the pitch of one of the strings S is raised by increasing the tension, the sum of the tension of all the strings S is increased. This pivots the tremolo body 120 toward the neck from the equilibrium position and thus shortens the distance between the nut and the string supports 121. Accordingly, the tension of other strings S is decreased and the pitches of the other strings S are lowered. When the tension of one of the strings S is decreased, the pitches of the other strings S are raised. Thus, it is theoretically impossible to perfectly tune all the strings S. To proximate the pitches to the perfectly tuned state requires much effort.
Further, a certain correspondence is established among a target pitch, the line density, and the length of each string S. However, the scale length of the above described tremolo unit 110, in which one end of each string S is movable, is changed depending on the strength of the springs 130. Therefore, when turning the open strings S, there are a number of neutral points at which an open string S is tuned outside the scale length. Therefore, if the tremolo unit 120 is inclined toward or away from the neck compared to the designed equilibrium position, the scale length is changed from the designed value, and the sound of a desired pitch cannot be produced when a string S is pressed against a certain fret on the neck.
The drawbacks of the tremolo unit 110 have attracted attention. Accordingly, tremolo units have been introduced in recent years having springs the tension of which is greater than those of strings. Japanese Laid-Open Patent Publication No. 1-93793 and Japanese Examined Patent Publication No. 2-48120 disclose such tremolo units. However, the mechanism disclosed in the publication No. 1-93793 requires a great force to increase the tensions of the strings to raise the pitch, or to manipulate the tremolo arm. In the tremolo unit disclosed in the publication No. 2-48120, the tremolo block is directly connected to one spring. Therefore, if the spring is inclined or deformed in a direction other than the expanding and contracting directions due to pivoting of the tremolo body, the resilience of the spring is affected. The tremolo unit has a stopper to limit the movement of the tremolo body. To reduce the noise produced by collision of the tremolo body against the stopper, a shock absorbing member, such as rubber, is located between the tremolo body and the stopper. In this case, deformation of the shock absorbing member is likely to detune the strings. Further, the tremolo unit has a number of adjusters. The locations of the adjusters are not easy to find and the procedure of adjustment is not easy to understand.
U.S. Pat. No. 4,928,564 discloses a tremolo unit having a bracket located between a tremolo block and a guitar body. A counter balance spring assembly is located on the bracket. The assembly includes a tube and a rod, which are attached to the bracket. The rod is received by the tube. One end of the rod is coupled to the tremolo block. As the tremolo block is moved, the rod moves relative to the tube, which applies an adequate tension to the tremolo arm.
The above described tremolo unit often makes players uncomfortable. For example, when the bridge or the tremolo block is returned to the neutral position, the arm cannot be smoothly manipulated. Therefore, players that prefer the feel of a floating bridge are disturbed. If the friction among the members in the counter balance spring assembly is transmitted to the player during performance of the instrument, the player may feel uncomfortable.
Accordingly, it is an objective of the present invention to provide a tremolo unit for string instrument that minimizes the degree of detuning, permits the strings to be easily and accurately tuned, and prevents a player from feeling uncomfortable during performance.
To achieve and foregoing and other objectives and in accordance with the purpose of the present invention, a tremolo unit applied to a string instrument having a base plate and a plurality of strings is provided. The base plate has a top surface and a back surface and is pivotally supported by a body. A front end of each string is supported by a neck, and a rear end of each string is supported by the top surface of the base plate. The tremolo unit permits the base plate to be pivoted in response to manipulation of a tremolo arm. The tremolo unit includes a tremolo block, a base, an engaging section, a moving member, a first spring, and a second spring. The tremolo block extends vertically from the back surface of the base plate into a space defined in the body and pivots with the base plate. The tremolo block has a hook portion at its distal end. The base is located at a back portion of the body. The engaging section is formed at a rear portion of the base and opens rearward. The moving member is detachably located at the engaging section. The moving member is moved between an engaging position, at which the moving member engages with the engaging section, and a standby position, at which the moving member is separated from the engaging section. The first spring connects the base with the tremolo block, and urges the tremolo block forward against tension of the strings. The urging force of the first spring is adjustable. The second spring connects the base with the moving member, and urges the moving member toward the engaging position. In a normal state, the second spring holds the moving member at the engaging position. When the tremolo block is stopped or pivoted forward, the moving member is held at the engaging position by the urging force of the second spring. When the tremolo block is pivoted rearward, the moving member is moved from the engaging position to the standby position by contact between the moving member and the hook portion.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.